[InstCombine] Add support for ptrtoaddr in pointer difference folds (#164428)

This adds support for folding `ptrtoaddr(p2) - ptrtoaddr(p)` pointer
subtractions. We can treat ptrtoaddr the same as ptrtoint as the
transform is truncation safe anyway (and in fact supports explicit
truncation as well).

The only interesting case is the subtraction of zext of ptrtoaddr. For
this transform it's important that the address bits are not truncated --
and if any pointer bits are truncated, that the truncation is consistent
for both operands. I've explicitly spelled out the three different cases
for this, which also fixes a miscompile in the existing ptrtoint fold.

0 files changed, 0 insertions, 0 deletions